1. Field of the Invention
The present invention relates to a voltage converting circuit, and more particularly, to a voltage converting circuit capable of improving power efficiency.
2. Description of the Prior Art
Generally speaking, supply voltages utilized by integrated circuit chips come from systems. For examples, supply voltages for network chips, wireless communication chips, or image processing chips disposed in desktop or laptop computers are provided by motherboards. However in general case, input voltages generated by systems are too high to be used directly as supply voltages in IC chips unless certain voltage converting circuits first convert input voltages into lower voltage level that suits IC's use.
Typical voltage converting circuits include switching regulators and linear regulators.
Switching regulators achieve high power efficiency. For example, if a 3V input voltage is to be converted into a 1.5V supply voltage, the switching regulator achieves high power efficiency, even close to 90%, but an off-chip inductor or capacitor is required. Off-chip components such as inductors or capacitors are not only expensive but also large in volume. Besides, the switching regulator causes ripple effect at the voltage output, and results in unstable output voltages.
Linear regulators utilize an off-chip bipolar junction transistor (BJT) to replace the off-chip inductor or capacitor. The BJT is much lower in price and causes few ripples. However, linear regulators have low power efficiency. For example, if the 3V input voltage is converted into the 1.5V supply voltage, the best power efficiency that linear regulators can achieve is only 50%.